In fields such as x-ray crystallography a narrow beam of x-rays are often diffracted from the crystalline structure under study. Often for practical reasons these beams are detected with large area detectors having areas many times the cross-sectional area of the beam being detected. The present invention provides methods of precisely locating the point of impingement of such beams on such large area detectors. These techniques or methods are simpler and involve less cost than previously known techniques for accomplishing this purpose. The techniques are applicable to any continuous particle or electromagnetic beam, e.g., light, molecular or electron beams, x-rays or gamma rays, etc.